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omshell

NAME

omshell - OMAPI Command Shell

SYNOPSIS

omshell

DESCRIPTION

The OMAPI Command Shell, omshell, provides an interactive way to connect to,
query, and possibly change, the ISC DHCP Server's state via OMAPI, the Object
Management API. By using OMAPI and omshell, you do not have to stop, make
changes, and then restart the DHCP server, but can make the changes
while the server is running. Omshell provides a way of accessing
OMAPI.

OMAPI is simply a communications mechanism that allows you to
manipulate objects. In order to actually use omshell, you
must
understand what objects are available and how to use them.
Documentation for OMAPI objects can be found in the documentation for
the server that provides them - for example, in the dhcpd(1)
manual page and the dhclient(1) manual page.

CONTRIBUTIONS

This software is free software. At various times its development has
been underwritten by various organizations, including the ISC and
Vixie Enterprises. The development of 3.0 has been funded almost
entirely by Nominum, Inc.

At this point development is being shepherded by Ted Lemon, and hosted
by the ISC, but the future of this project depends on you. If you
have features you want, please consider implementing them.

LOCAL AND REMOTE OBJECTS

Throughout this document, there are references to local and remote objects.
Local objects are ones created in omshell with the new command. Remote
objects are ones on the server: leases, hosts, and groups that the DHCP
server knows about. Local and remote objects are associated together to
enable viewing and modification of object attributes. Also, new remote
objects can be created to match local objects.

OPENING A CONNECTION

omshell is started from the command line. Once omshell is started, there are
several commands that can be issued:

server address

where address is the IP address of the DHCP server to connect to. If this is
not specified, the default server is 127.0.0.1 (localhost).

port number

where number is the port that OMAPI listens on. By default, this is 7911.

key name secret

This specifies the TSIG key to use to authenticate the OMAPI transactions.
name is the name of a key defined in dhcpd.conf with the
omapi-key statement. The secret is the secret key generated from
dnssec-keygen or another key generation program.

connect

This starts the OMAPI connection to the server as specified by the server
statement.

CREATING LOCAL OBJECTS

Any object defined in OMAPI can be created, queried, and/or modified. The
object types available to OMAPI are defined in dhcpd(8) and
dhclient(8). When using omshell, objects are first defined locally,
manipulated as desired, and then associated with an object on the server.
Only one object can be manipulated at a time. To create a local object, use

new object-type

object-type is one of group, host, or lease.

At this point, you now have an object that you can set properties on. For
example, if a new lease object was created with new lease, any of a
lease's attributes can be set as follows:

set attribute-name = value

Attribute names are defined in dhcpd(8) and dhclient(8).
Values should be quoted if they are strings. So, to set a lease's IP address,
you would do the following:
set ip-address = 192.168.4.50

ASSOCIATING LOCAL AND REMOTE OBJECTS

At this point, you can query the server for information about this lease, by

open

Now, the local lease object you created and set the IP address for is associated
with the corresponding lease object on the DHCP server. All of the lease
attributes from the DHCP server are now also the attributes on the local
object, and will be shown in omshell.

VIEWING A REMOTE OBJECT

To query a lease of address 192.168.4.50, and find out its attributes, after
connecting to the server, take the following steps:

new lease

This creates a new local lease object.

set ip-address = 192.168.4.50

This sets the local object's IP address to be 192.168.4.50

open

Now, if a lease with that IP address exists, you will see all the information
the DHCP server has about that particular lease. Any data that isn't readily
printable text will show up in colon-separated hexadecimal values. In this
example, output back from the server for the entire transaction might look
like this:

As you can see here, the IP address is represented in hexadecimal, as are the
starting and ending times of the lease.

MODIFYING A REMOTE OBJECT

Attributes of remote objects are updated by using the set command as
before, and then issuing an update command. The set command sets
the attributes on the current local object, and the update command
pushes those changes out to the server.

Continuing with the previous example, if a set client-hostname =
"something-else" was issued, followed by an update command, the
output would look about like this:

NEW REMOTE OBJECTS

New remote objects are created much in the same way that existing server
objects are modified. Create a local object using new, set the
attributes as you'd wish them to be, and then create the remote object with
the same properties by using

create

Now a new object exists on the DHCP server which matches the properties that
you gave your local object. Objects created via OMAPI are saved into the
dhcpd.leases file.

For example, if a new host with the IP address of 192.168.4.40 needs to be
created it would be done as follows:

The dynamic; line is to denote that this host entry did not come from
dhcpd.conf, but was created dynamically via OMAPI.

RESETTING ATTRIBUTES

If you want to remove an attribute from an object, you can do this with the
unset command. Once you have unset an attribute, you must use the
update command to update the remote object. So, if the host "some-host"
from the previous example will not have a static IP address anymore, the
commands in omshell would look like this:

REFRESHING OBJECTS

A local object may be refreshed with the current remote object properties
using the refresh command. This is useful for object that change
periodically, like leases, to see if they have been updated. This isn't
particularly useful for hosts.

DELETING OBJECTS

Any remote object that can be created can also be destroyed. This is done by
creating a new local object, setting attributes, associating the local and
remote object using open, and then using the remove command.
If the host "some-host" from before was created in error, this could be
corrected as follows:

HELP

SEE ALSO

AUTHOR

omshell
was written by Ted Lemon of Nominum, Inc. Information about Nominum
can be found at
http://www.nominum.com.
This preliminary documentation was written by Wendy Verschoor of Nominum,
Inc., while she was testing omshell.